The present invention relate to a recording apparatus which records an image by ejecting recording liquid such as ink, in the form of a droplet, from its ejection orifices. It also relates to an ink jet recording head used for such a recording apparatus. Not only can an ink jet recording head in accordance with the present invention be usable with an ordinary printing apparatus, but also with such an apparatus as a copying machine, a a facsimile machine equipped with a communication system, or a word processor equipped with a printing portion, or an industrial recording apparatus intricately combined with various processing apparatuses. An ink jet recording apparatus is a recording apparatus based on a so-called nonimpact recording method. It is characterized that it is capable of recording on various recording media at a high speed, and makes virtually no noises while recording. Thus, an ink jet recording apparatus is widely used as an apparatus which plays a role of a recording mechanism in a printer, a copy machine, a facsimile machine, or a word processor.
Known as a typical ink ejecting method for a recording head mounted in an ink jet recording apparatus such as the one described above are a method which employs electromechanical transducers such as a piezoelectric element, a method which employs an electromagnetic device such as a laser, a method which employs electrothermal transducers having a heat generating resistor, and the like methods. In a method employing an electromagnetic device, electromagnetic waves are irradiated to generate heat, which is used to eject ink droplets, whereas in a method employing electrothermal transducers, ink is heated with the electrothermal transducers, to a point of film-boiling so that ink droplets are ejected. In an ink jet recording head which employs electrothermal transducers, the electrothermal transducers are disposed within a recording liquid chamber, and electrical pulses as recording signals are supplied to the electrothermal transducers to generate heat to give ink thermal energy. As thermal energy is given to ink, that is, recording liquid, the ink changes in state, generating bubbles therein, and the pressure generated as a bubble grows is used to eject microscopic droplets of ink from microscopic orifices onto recording medium, As a result, an image is formed on the recording medium.
Generally, an ink jet recording head has a plurality of recording nozzles for ejecting ink droplets, and a supply system for supplying the recording nozzles with ink.
A recording apparatus equipped with an ink jet recording head such as the one described above can inexpensively output a high quality image inclusive of both a character and a graphic image.
An ink jet recording apparatus is convenient in that it is inexpensive and is capable of outputting a color print. Therefore, an ink jet recording apparatus, in particular, an ink jet recording apparatus based on a bubble-jet method (which hereinafter will be referred to as BJ method) which employs the liquid ejection principle proposed by Canon Inc., that is, the applicant of the present invention, has been occupying the major portion of the printer market. According to the BJ method, liquid is heated to a point of film-boiling so that liquid is ejected by bubble formation (generation, growth, contraction, and extinction). This type of a printer has a black, cyan, magenta, and yellow ink ejecting head portions, all of which employ a bubble-jet method.
There is a general tendency that the number of the ejection orifices of each head portion is increased to improve image quality: it has been increased from 64 to 128, 256, or the like, which is equivalent to 300, 600, and the like, equivalent to a resolution of 300 dpi, 600 dpi, or the like, or the number of dots per inch: in other words, ejection orifices are disposed at a very high density. Also in each head portion, a plurality of electrothermal transducers as heating elements are disposed in a manner to oppose these ejection orifices. An electrothermal transducer is driven by a pulse, the duration of which is in the order of several microseconds to 10 microseconds, to heat ink to the point of film-boiling to form a bubble in the ink. In other words, it can be driven at a very high frequency to print a high quality image at a high speed. In recent years, there has been a tendency to increase the number of the heating elements to be driven per unit of time, in order to further improve the performance of the head portion.
Recently, a new type of a printer which a employs an air/bubble connection method, that is, the so-called bubble-through-jet method (which hereinafter will be referred to as BTJ method), has been introduced into the market. This bubble-through-jet system is a new type, or an improved type, of the above described bubble-jet system, which also was proposed by the applicant of the present invention. According to this type, the aforementioned bubble is allowed to become integrated with the atmospheric air in order to stabilize liquid a droplet size, so that microscopic liquid droplets uniform in size can be ejected. This type of a printer also has black, cyan, magenta, and yellow liquid ejecting head portions, all of which employ a BTJ methods, as all the ink ejecting head portions of the aforementioned bubble-jet printer employ a bubble-jet method. In other words, this BTJ type printer outputs an image higher in quality than the image outputted by a conventional bubble-jet printer, by ejecting microscopic liquid droplets uniform in size. The advantages of this new printer are as follows.
In order to achieve color recording quality as high as that of silver salt photography, a picture dot must be small enough to be unrecognizable as a dot on recording medium (not large enough to make an image look grainy).
Therefore, the size of a color ink droplet is set to approximately 5 pl (pico-liter or 1012 liter) in volume, 40-50 xcexcm in diameter, or 600xc3x971,200xe2x80x941,200xe2x80x941,200 dpi (dpi is a unit which shows the number of dots per inch) in resolution. In consideration of the fact that the improvement in resolution and sharpness must be also made for a character printed in black ink, it is necessary to form a smaller dot by ejecting a smaller liquid droplet. However, black ink is often used to create a solid image, that is, an area solidly covered with black ink, in addition to recording letters or the like.
If a solid image is printed by ejecting microscopic liquid droplets, the number of times liquid must be ejected becomes rather large, and therefore, recording time tends to become longer. Thus, it is to be desired that the ink droplet size for black ink should be set to a larger one compared to that for color ink, for example, 30 pl in volume, 80 xcexcm in diameter, or 600 dpi in resolution.
As for the method for differentiating color ink (cyan, magenta, or yellow ink) from black ink, in liquid size or volume, increasing ejection orifice size, and modifying liquid flow path design, have been known. These methods, however, have created new problems in terms of the overall performance of a printer.
That is, the application of a design for forming a microscopic liquid droplet to the aforementioned black, cyan, magenta, and yellow ink ejecting portions which employ the aforementioned BTJ method, results in variance in ejection velocity and liquid droplet volume, tending to make the color ink ejecting portions about the same as, or inferior to, the black ink ejecting portion, in terms of the accuracy with which an ink droplet lands on a predetermined point on recording medium.
On the other hand, the volume of a black ink droplet to be ejected from a recording head comprising black, cyan, magenta, and yellow ink ejection portions which employ the aformentioned BTJ system, can be increased by increasing the size of a heater, of electrothermal transducer, and the size of the ejection orifice. However, this makes it impossible to increase the driving frequency, and therefore, increases the amount of mist created during liquid ejection.
In both cases, it is possible to individually redesign each liquid ejecting portion. However, as the frequency at which the heaters are driven per unit of time when these liquid ejecting portions are in a printer has been gradually increased, the number of the heaters which can be employed has reached a limit, making it impossible to provide a high density recording head which can be efficiently driven. In addition, from the standpoint of realizing an ejection velocity higher than a predetermined level, and also the standpoint of stabilizing liquid droplet size, it has become evident that it is very difficult to realize a printer in which both the black ink ejecting portion and color ink ejecting portions perform at their satisfactory performance levels. As for a printer design for solving the above described problem, it is possible to increase electrical power source capacity or the number of electrical power sources, as is obvious. Such a design, however, makes a printer extremely expensive and large, which is not practical.
Thus, the inventors of the present invention studies the above described problems, and searched for solutions therefor. More specifically, the inventors studied the interaction of the black ink ejecting system and color ink ejecting system, in terms of ejection volume, ejection velocity, and ejection stability, instead of studying them individually. As a result, the inventors discovered that the above described secondary problem which is caused by the solutions to the primary problems, can be solved by making the black ink ejection portion different from the color ink ejection portions, in ejection method itself. Further, in order to reduce the head portion size relative to a printer and to improve the accuracy with which head portions are aligned as they are mounted into a printer, the inventors toiled to simplify the head portion structure, and also to provide a production method compatible with such a structure. As a result, the inventors came up with an idea of placing the black ink ejecting portion and color ink ejecting portion on the same member, and aligning them with reference to a common referential surface.
Accordingly, a primary object of the present invention is to provided an ink jet recording head and a recording apparatus, which are capable of recording in both black mode and color mode, while accomplishing high density and high quality in both modes, and also are low in cost, small in size, and simple in structure.
According to an aspect of the present invention, there is provided an ink jet recording head comprising a plurality of recording element substrates each having a plurality of recording elements for applying ejection energy to recording liquid; a plurality of flow paths for the recording liquid which is to receive ejection energy; a supply port for supplying the recording liquid to the plurality of flow paths; a plurality of ejection outlets for ejecting the recording liquid, said ejection outlets being disposed face to the recording elements, respectively; wherein distances between the recording elements and the ejection outlets in at least one of said recording element substrates are different from distances between the recording elements and ejection outlets of another one of said recording element substrates, and wherein liquid ejection systems of the recording elements of said at least one of said recording element substrates and the recording elements of said another one of said recording element substrates, are different.
It is preferable that the distances between said recording elements and said ejection outlets in said at least one of said recording element substrates to which blackish liquid is supplied is longer than the distances between said recording elements and said ejection outlets in said another one of said recording element substrates to which chromatic liquid is supplied.
It is preferable that liquid ejection amounts from said ejection outlets in said at least one of said recording element substrates to which blackish liquid is supplied is larger than the liquid ejection amounts from said erection outlets in said another one of said recording element substrates to which chromatic liquid is supplied.
It is preferable that a density of arrangement of said recording elements in said recording element substrates to which the chromatic liquid is supplied is approx. Two times the density of arrangement of said recording elements in said recording elements substrates to which the blackish liquid is supplied. By doing so, the recording elements for the black color and the recording elements for the chromatic color can be actuated at the same frequencies, and therefore, the high-speed printing is accomplished with a simple structure and without degrading the durability.
With such a structure, it is possible that the black droplet may be large so that solid black can be printed at a high speed, while the chromatic color droplet may be small so that high-resolution color printing is accomplished.
It is preferable that the liquid ejection system of the recording elements of said at least one of said recording element substrates is such that bubbles are generated in the recording liquid by actuation of said recording elements, and the bubbles are collapsed, and the liquid ejection system of the recording elements of the recording elements of said another one of said recording element substrates is such that bubbles are generated in the recording liquid by actuation of said recording elements, and the bubbles are brought into communication with ambience.
With the structure, after the color recording liquid is ejected out, the bubble pressure escapes to the outside, and therefore, the vibration of the meniscus is small, so that high speed liquid refilling is accomplished.
It is preferable that said recording element substrates have base plates having substantially the same thicknesses and placed on one flat surface and have ejection outlet forming members laminated on the base plates, and wherein said at least one of said recording element substrates have different heights of the ejection outlet forming member, by which the distances between said recording elements and said ejection outlets are different from the distances between said recording elements and said ejection outlets in said another one of said recording element substrates.
It is preferable that said recording element substrates have base plates having substantially the same thicknesses and placed on one flat surface and have ejection outlet forming members laminated on the base plates, and wherein said ejection outlets are formed by photo-patterning.
It is preferable that the distances between said recording elements and said ejection outlets in said at least one of said recording element substrates are not more than 100 xcexcm.
It is preferable that a liquid ejection speed VBk and a liquid ejection amount V-dBk through said ejection outlets in said at least one of said recording element substrates, and a liquid ejection speed VCl and a liquid ejection amount V dCl through said ejection outlets in said another one of said recording element substrates, satisfy;
vCl greater than VBkxe2x89xa78 m/sec, 
and
vdBk greater than V dCl. 
It is preferable that the distances O HBk between said recording elements and said ejection outlets and distances hBk between said recording elements and said ejection outlet forming member in said at least one of said recording element substrates, and the distances OHCl between said recording elements and said ejection outlets and distances hCl between said recording elements and said ejection outlet forming member in said another one of said recording element substrates, satisfy;
hBk greater than h Cl, 
and
oHBk greater than hBkxc3x972. 
It is preferable that there are provided a plurality of ink containers for supplying the recording liquids to said ink jet recording head and to said recording element substrates.
It is preferable that go to sleep and said recording elements are supplied with electric energy from one voltage source.